The present invention is related to a communication system comprising a transmitter for transmitting cyclically a plurality of mutually related objects via a communication network to a terminal, said terminal comprising processing means for processing said plurality of mutually related objects.
The present invention is also related to a transmitter, a receiver, a method, a signal and a program stored on a tangible medium which can be used in such a system.
Such a system is known from the document ISO/IEC 13522-5:1996(E) xe2x80x9cMHEG-5 IS Document Second Draftxe2x80x9d Chapter 5, xe2x80x9cOverview of the MHEG-5 Classesxe2x80x9d, pp. 8-13.
The MHEG standard under development by ISO""s Multimedia Hypermedia Experts Group defines a system independent encoding of the data structures used for storing, exchanging and executing multimedia presentations. The MHEG standard is very suitable for the broadcast environment. In such a broadcast environment objects are transmitted cyclically in order to enable the user to retrieve these objects, independent from the instant the terminal is switched on. A first example application is a xe2x80x9cStock tradingxe2x80x9d application in which regularly updated stock quotes are displayed. A second example application is a xe2x80x9cHorse bettingxe2x80x9d application in which all horses in a selected race are shown together with information such as the winning odds per horse. In both applications the information is updated regularly. It is required that the information displayed in an application said applications is consistent, meaning that it has to be ensured that all information displayed have a common property. This property can be the time at which the information is established, as it is the case in the xe2x80x9cStock tradingxe2x80x9d and xe2x80x9cHorse bettingxe2x80x9d applications.
Presently the communication system according to the above mentioned publication has no provisions to ensure the consistency of the mutually related objects. In such a system the processing means extract objects from the received signal and processes them without knowing whether these objects are still consistent with other objects already present in the running application. In the xe2x80x9cStock trading applicationxe2x80x9d this can lead to stock prices established at different times to be displayed together as if they were established at the same time. Acting on such information could result into substantial damage for the user.
The object of the present invention is to provide a communication system in which the consistency of the mutually related objects is ensured.
To achieve said objective the communication system according to the invention is characterized in that the transmitter comprises assembling means for combining said mutually related objects into a combined transport entity, the processing means being arranged for extracting said plurality of mutually related objects from the common transport entity and for processing said plurality of said mutually related objects.
By combining the mutually related objects into a common transport entity, all mutually related objects are received simultaneously. By extracting said mutually related objects from the common transport entity and processing said mutually related objects together, consistency is ensured.
An additional advantage of using a transport entity comprising a plurality of objects is that the overhead required for transporting the objects is reduced.
An embodiment of the invention is characterized in that said transmitter is arranged for introducing into the combined transport entity an update indicator to indicate that the combined transport entity is updated, and in that the processing means being arranged for extracting said updated objects from the common transport entity if an update is indicated.
By introducing an update indicator, the processing means can easily determine whether the transport entity carries updated objects. If this is the case, the processing means extracts the updated values from the transport entity. Otherwise the processing means can ignore the objects, because they are the same as those already processed by the processing means. This leads to a considerable reduction of the required processing power.
A further embodiment of the invention is characterized in that the transport entity comprises a header indicating the size of the header and the size of the objects combined into said transport entity, and in that the update indicator comprises a version number.
By indicating the size of the different elements of the transport entity, such as header and objects, the position of each element in the transport entity can be calculated easily. An advantage of indicating the size of the different elements instead of indicating their absolute position in the transport entity is the reduced amount of data required to indicate the position of the objects in the transport entity.